Field of the Invention
Embodiments of the present invention generally relate to a support ring to support a substrate in a process chamber.
Description of the Related Art
In the processing of substrates, such as semiconducting substrates, the substrate is placed on a support in a process chamber and suitable processing conditions are maintained in the process chamber. For example, the substrate can be heated in a controlled heating cycle to thermally process the substrate. The substrate can be heated, for example, by an array of heating lamps disposed above and/or below the substrate in the chamber. Thermal processing can be used to anneal a layer that has been ion-implanted on the substrate, perform thermal oxidation or nitridation processes, or perform thermal chemical vapor deposition processes on the substrate.
It has been observed that variations in temperature gradients across the substrate can result in non-uniform processing of the substrate. Non-uniform temperatures occur at different substrate regions because of non-uniform convection or conduction heat losses or gains from regions of the substrate in contact with the support (or other chamber components) versus substrate regions not in contact with the support. Temperature gradients in substrates have been reduced using a substrate support ring that extends inwardly from the chamber wall and surrounds a periphery of the substrate. Particularly, the substrate to be thermally processed is supported on its periphery by an edge of the support ring having an annular lip contacting the edge of the substrate. The support ring effectively expands or pushes out the temperature gradients in the substrate from the substrate periphery to the outer edges of the support ring. The overlapping of the substrate and the support ring also prevents or minimizes the leakage of the high-temperature radiant energy from the radiant heat source (typically disposed above the substrate) around the edge of the support ring on either its inner or outer side.
Support rings having an annular edge can fail to provide adequate temperature uniformity across the substrate in rapid heating rate processes, for example, processes having heating rates of at least about 200° C./second in a rapid thermal processing (RTP) system. In these processes, the difference in heating rates between the support ring and the substrate generates temperature gradients along the periphery of the substrate that become unacceptably high during the heating process step. It is particularly difficult to achieve temperature uniformity across the substrate especially when the substrate is heated at reduced pressure. This is because the contact resistance at the overlapping area between the substrate and the support ring is much larger at lower pressure (since flow through the intimate contact points is dominant), causing the temperature profile at the edge of the substrate to be significantly higher than that at the central area.
Accordingly, it is desirable to have a support ring that facilitates a more uniform temperature gradient of substrates during processing.